High speed diesel engines for vehicular service are required to operate efficiently and with low emissions over a wide range of speeds. Also, means are frequently employed to increase the density, and therefore the available mass, of oxygen in the cylinder to increase the power output of the engine with minimum increase of engine size and weight. The combined effect is to require the fuel pump to deliver a wide range of quantities of fuel per stroke as well as over a large range of operating speeds. Since the resistance to flow of a fluid through the orifice of injection system nozzles varies as the square of the flow rate, delivery pressures up to 15,000 psi are frequently required if delivery periods are to be short at high speed and spray atomization adequate at starting and low idle speeds.
One of the means employed to determine and modulate the length of the part of the stroke of a fuel pump plunger during which the fuel is delivered at high pressure to an internal combustion engine is a sleeve member on the plunger. This sleeve is separate from the fixed cylinder in which pumping occurs. Both the sleeve and the fixed cylinder are subjected to high pressure within their precision bores during injection. Such pressure causes the bores to enlarge sufficiently to significantly increase the clearance around the plunger. Fuel under pressure flows through this clearance as leakage. Such leakage is unwanted as it reduces to an unacceptable degree the quantity and rate of fuel delivery to the engine at high loads and speeds.
The reciprocating pump plunger, its fixed mating cylinder or barrel, and metering sleeve are conventionally made of high strength steel with very accurately produced, smoothly finished and very hard mating cylindrical surfaces. They are fitted as closely as precision commercial grinding and lapping operations make feasible. Out-of-round, taper, straightness, and surface roughness are all closely controlled on each piece and then they are sorted for size and selectively assembled. The working clearances of the parts are thus held at the minimum achievable by feasible manufacturing techniques.
Although injection pumps incorporating sleeves for metering have demonstrated advantages in ease of control and in low production costs, so far their use has largely been limited to engines having only modest peak injection pressure requirements; i.e., less than 10,000 psi.
In general, the invention relates to fuel injection pumps for internal combustion engines and more particularly to pumps capable of delivering liquid fuels at high pressures as required for most efficient and clean combustion of supercharged diesel engines of the compact, high speed type used to power vehicles. This invention is also particularly applicable to reciprocating plunger fuel injection pumps employing a separately movable sleeve for metering and/or timing control. Leakage of fuel from the high pressure pumping circuit of such pumps is substantially reduced by employing either individually, or in combination, means to add restraint to change in diameter of parts in an unusually effective way or to provide means for enlargement of the pump plunger sufficiently to match enlargement of the bore in which it works. Since working pressures are of a magnitude that is a significant fraction of the fatigue stress limit of heat treated high strength steel, proportions of the components of this invention are such as to avoid the over stressing of them.
One objective is to provide restraint against enlargement of the bore of a cylinder subjected to internal pressures by axially extending its relatively thick wall beyond the portion of it subjected to internal pressure to provide a non-pressurized contiguous structure.
Furthermore, wherever possible, such by-pass means as may be required, which is caused to be closed by plunger motion at start of the fuel delivery cycle, is in the well-known form of a single port in the barrel wall positioned to be closed by the end of the plunger so that pressure in the cylinder acts to press the plunger against the cylinder wall around said port and thus minimize leakage.
Since the foregoing means to minimize leakage is not effective within the sleeve but instead pressure in the system pushes the sleeve away from the port, another objective of this invention is to provide a plunger with a wall of sufficient thinness that it will be enlarged by the injection pressure within it in the area extending outside of the sleeve and fixed cylinder sealing sections, but such plunger wall still of sufficient thickness to enlarge with it that portion of the plunger still within the sealing areas sufficiently to cause a net enlargement of the plunger essentially equal to that of both the sleeve and the fixed cylinder. By these means the actual working clearance will be as slight when working at pressures up to 15,000 psi as at low or zero pressure.
A further objective is to accomplish the above with peak cycle stresses at acceptable levels for essentially infinite fatigue life and to do so with a construction that will be easily made at lower costs than other sleeve metering designs, and in all other aspects be equivalent or superior to those made according to known art and practices.
Sleeve metering pumps are prone to certain unique problems of control and governing as the result of uneven (and sometimes even) transmission of oscillating forces to their controlling mechanism which may resonate or otherwise improperly react to them. These oscillating forces originate from drag of the plungers within the sleeves. As a practical matter, not all plungers and sleeves can be manufactured to have identical fit and finish. The more closely the pair are fitted, the more apparent variations become. If as a result of an adverse combination of tolerances, a sleeve fits too closely, the reciprocating motion of that plunger will produce excessive oscillating forces on its sleeve which through its positioning lever then act on the governor or control mechanism. An object of this invention, then, is to reduce the necessity for excessively close fit of sleeves and plungers as assembled but provide an adequate control of clearance for leakage control by other means. Thus governing and control problems can be alleviated.